Process of drying artificial silk



JZAWAQL I E. BRONNERT' PROCESS OF DRYING ARTIFICIAL SILK.

APPLICATION FILED SEPT. 3, 1920.

YL-wtented Dec. 5, 13 22.

W Patented Dec. 5, 1922.

D A E EMILE BBONNERT, or MUnHAusEn, ALsAcn-LonnAiNE, FRANCE.

' rz'aocnss or DRYING nn'rxrrcmi. SILK.

\ Application filed September 3, 1920. Serial No. 408,037.

"To all wh om it may concern:- I

- Be itknown that I, EMILE-BRoNNIRT, a citizen of the Republic of'France, residing at 1 Quai du Barrage, Mulhausen, Alsace- 5 Lorraine France, have invented certain new 'and useful Improvements in Processes of Drying Artificial Silk, of which-the follow- 'ing is a specification. Y

' This invention relates to a rapid drying in process for freshly precipitated cellulose hydrate. threads. 1 v

As is" well known, there exists a very great difierence in the time necessary for drying a freshly precipitated more or less gelatinous thread of cellulose hydrate r and that necessary for the same thread, which, after the first drying process, is again saturated with water and dried under the otherwise usual conditions.- Ilhe first-named sort of gelatinous threads especially must be preserved from being weakened or from taking a brownish. color, dueto decomposition of the hydrate of cellulofie.

The difference 1 time necessary for drying is due to the fact that Water diffuses much more rapidly from artificial silk thread which has once been fixed by.drying than from the colloidal and gelatinous thread freshly precipitated or even from the thread which is approaching the normal solid state upon progressivedrying. Difj ferences of permeability of the material in a different physical state, and different strength of capillary forces may be the ssreasons of this phenomenon.

The insufiicient attentlon given to these considerations has given rise to the very uneconomical and "tedious arrangements hitherto used for drying fresh gelatinous threads of cellulose hydrates. These threads are mostly wound'upon rollers or spools of glass, metal or other acid-proof, water-proof and heat-resisting material in relatively thin layers and piled up -in ventilated and warmed roomsm It has already been pro posed to-make this storage or stacking up in v a different chambers and to use over again the air that has been cooled by the evaporation of water in one chamber, by rte-heating it up. to the temperature normally used. The,

' counter-current principle has also been emjployed,-but* thefdry1 ng process lasted for days, the temperature scarcely exceeding to (3., so that this plan was not eco- 55 nomical.

lhe reluctance to adopt other means is undoubtedly to be attributed to the fact that the soft thread quickly changed color and became brown when the temperature' was raised higher than '60 to 70 0., like a damp white cotton fabric brought into contact with too hot an iron. Upon dyeing these :damaged threads with suitable dyes (for example methylene blue) it was demonstrable'. that a chemical change .had taken place at the" said points. This change happened especi lly on the outer layerof the threads on the spool, [when the latter had stood too near to the radiator. was deduced that the soft texture of the threads could not stand any high temperature, while according topresent-day observation the fault was, undoubtedly due to differences in the temperature of the heated air in the same cross section o-f the apparatus, that is, to a want of perfect thermal equilibrium of the air in the said section.

It was the large production, in recent times, of such threads as the so-called staple fibres, wool substitute, and the like, which once again compelled attention to be given, on thebasis of fundamentally new considprocess. 7 p

Hence this invention consists in the proc ess, for drying cellulose hydrate filaments, by employing temperatures higher than have hitherto ,been held to be applicable, without impairing them. This is accomplished by using a strong current of air, care being taken by proper measures that the contact of theair with the threads is as intimate as possible and that at any given time, in any cross section of the apparatus, the temperatureis perfectly uniform. The threads-may if preferred be wound on rollers in the known manner indicated above,

From this it -erations, tothe search for a better drying but the invention is in no way limited to the drying of threads so wound. I

In the event of theidrying operation proceeding by steps, the air coming vfrom one step or chamber has to be heated up again to the hi her temperature and thoroughly mixed beore being blown again upon the threads.

Of course the highest admissiblev temperature .given' to the current of air cannot be maintained throughout all the apparatus, but exists onlyat theentrance to each new step, when the air coming from the step before has been heated up again" and reaches the threads. In eachsubsequent cross sec tion of chamber transverse to the flow of air the temperature is lowered as long as there is moisture to be evaporated, but the strong current of air and the measures taken for thorough mixing and intimate contact have to ensure that the temperatures are perfectly uniform to each cross section, though varying from one cross-section to another.

A hlgh temperature of course ensures quick and very economical drying, as hot air takes up and carries away incomparably more water than cooler air. This economy was to be expected on theoretical grounds; but for a long time no one thought of employing a higher temperature in practice, as in experiments an impairing of the dried material was always observed.

In the accompanying drawings various forms of drying apparatus are illustrated in which my process may be practiced.

Figure 1 is a diagrammatic longtiudinal section of such apparatus.

Figs. 2, 3 and 4 are similar views of other forms of such apparatus.

According to Fig. 1', the drying passage is provided with vertical walls 0 which are perforated to allow air to pass and which form the drying chambers 0;, wherein the materialto be dried is placed. Between each pair ofwalls c a'space is left for the reception of heating coils 6,. The perforated walls a, may consist of lattice work or of perforated plates. The air flows in the direction of the arrows through the various chambers. The air which has been cooled in the first chamber by drying the material deposited therein, is, upon passing out of the chamber into the next chamber not only quite uniformly heated by the heating coi 6,, but also, in consequence of the numerous uniformly distributed openings in the walls 0 is thoroughly mixed, so that only air which has been uniformly heated in all parts and is therefore in thermal equilibrium is admitted to the material deposited in the chamber next in line. cedure is followed in the subsequent cham bers formed by the spaced walls separating them.

In the construction of the apparatus illustrated in Fig. 2, the tops andthe bottoms of the drying chambers a are formed of perforated Walls 0 and the heating coils 6 are accommodated in between spaced impervious walls between the chambers a and which separate the drying chambers from one another. In the case of this arrangement also, the current of air, in passing through the horizontal perforated ,walls 0 is so mixed that it enters the drying chamhers in a uniformly heated condition.

ile in the apparatus according to Fig. 2, the air in all the drying chambers flows from above downwards, in that according to Fig. 3, the air in the drying chambers will .the invention may be carried out The same pro-.

flow alternately downwards and upwards. In this form of apparatus the heating coils Z2 are housed in special communication passages which are arranged at the top of the apparatus. The air flowing downwards out of one chamber a passes through the perforated walls 0 at the bottom into the next chamber through the upper perforated wall and the aperture i into the heating passage, is here heated up again and then flows through the aperture Z and the upper per-. forated Wall of the drying chamber into the latter chamber and so forth. Hence in this case the re-heating of the air only takes place once for every other chamber.

In Fig. 4 similar heating passages are also arranged at the bottom of the apparatus, so that the air will be pro-heated before entering every chamber, as will at once be obvious.

Arrangements may be made if desired for removing the material which is first dried without waiting. until all the fibres in all the chambers are ready for removal, or for shifting the material from one chamber to another in any well known manner, or disconnecting the chambers singly from the hot-air circuit. Such arragements however form no part of the invention, as the threads exposed to the hottest and driest air may quite safely be left there until the drying is completed throughout.

The dimensions of the chambers, and the number of times the same air maygadvantageously be reheated, will naturally vary according to circumstances and will be determined by calculation or experience. Probably from four .to eight chambers might be conveniently used and in any case the number is not likely to be much greater than ten. On the other hand it will be borne in mind that the process according to in a single chamber without any second heating of the 3.11:

Trials made with air which has been heated to a temperature of from 100 to 130 or even 140 C. showed that it was quite possible to dry, under the conditions prescribed, at this higher and therfore more economincal temperature. The means of realizing these conditions are generally known and are not claimed in conjunction with this invention. It will be understood that gases other than air which do not affect cellulose may be employed in this process, and when I speak of air in the claims such other gases are included.

What I claimis:

1. The step in the process of producing artificial silk which comprises subjecting gelatinous cellulose hydrate to the action of a continuously moving current of hot air, of a temperature of 100 C. to 140 C.

2. The step in the process of producing artifical silk which comprises subjecting:

freshly precipitated more or less gelatinous cellulose hydrate to the action of a continuously moving strong current of hot air, of a temperature of 100 C. to 140 0., the said current of air being brought into intimate contact With the threads and its temperature at any given time being substantially the same at all parts of any given signed my name in the presence of two subscribing Witnesses.

I EMILE BRONNERT. 

